As LCDs, one of many types of image displays, have been technically improved to provide wide viewing angles, high resolution, high response, good color reproduction, and the like, applications of LCDs are spreading from laptop personal computers and monitors to television sets. In a basic LCD structure, a pair of flat glass substrates each provided with a transparent electrode are opposed via a spacer to form a constant gap, between which a liquid crystal material is placed and sealed to form a liquid crystal cell, and a polarizing plate is formed on the outside surface of each of the pair of glass substrates. In a conventional method for performing antiglare treatment, the surface of a polarizing plate having a sandwich structure of two transparent plastic film substrates is roughened by an appropriate process such as sand blasting, roll embossing and chemical etching so as to have fine irregularities, or a hard coat layer containing dispersed fine particles is additionally provided on the surface of a transparent plastic film substrate to form fine irregularities.
An antiglare hard-coated film having an antiglare-treated transparent plastic film substrate is generally obtained by forming, on a transparent plastic film substrate, a thin coating film with a thickness of about 2 to 10 μm comprising a thermosetting resin or a ionizing radiation-curable resin such as an ultraviolet-curable resin and spherical or indefinite form inorganic or organic fine particles with particle sizes of several μm dispersed in the resin.
As flat panel displays such as LCDs have been used for home television sets, there have been demands for improved display qualities such as wide viewing angle, high response speed and high definition and demands for improved antiglare properties for preventing reflection of a room fluorescent light or the figure of a viewer on the surface of a display and for a further improvement in display contrast at a bright place, namely an improvement in the density of the displayed black.
However, there is a trade-off relationship between antiglare properties and display contrast. In display contrast-oriented applications, therefore, a hard coat layer with a smooth surface is placed on the uppermost surface of a display screen at the expense of antiglare properties. In antiglare properties-oriented applications, an irregular hard coat layer (an antiglare layer) is placed on the uppermost surface of a display screen.
The reflection from the smooth surface of a hard coat layer or from the surface of an antiglare layer and the effect of light scattering in the interior of an antiglare layer are believed to be causes of a reduction in display contrast at a bright place. An antireflection layer for preventing a surface reflection-induced reduction in display contrast may be appropriately provided on the uppermost surface of a display screen so that the reflection of external light from the display screen can be reduced, and thus display contrast at a bright place can be improved.
The trade-off relationship cannot be avoided even when an antiglare hard coat layer obtained by adding fine particles to a hard coat resin is simply used. This is because display contrast can be reduced when the amount of the addition of the fine particles is controlled as needed in order to achieve the desired antiglare properties. For example, Patent Literature 1 shown below discloses a method for solving the problem about the display contrast reduction in such an antiglare hard-coated film.
Patent Literature 1 discloses an antiglare antireflection film including a transparent support and at least one antiglare hard coat layer provided thereon. The antiglare hard coat layer includes at least one type of first optically-transparent particles having an average particle size of at least 60% and less than 95% of the thickness of the antiglare hard coat layer and at least one type of second optically-transparent particles having an average particle size of at least 105% and less than 140% of the layer thickness. In the antiglare antireflection film with such a structure, however, it is difficult to improve both of the display contrast and antiglare properties at the same time only by means of the average particle sizes of the optically-transparent fine particles specified relative to the thickness of the hard coat layer.    Patent Literature 1: Japanese Patent Application Laid-Open No. 2003-248110